Research On The Organic Rankine Cycle System For The Waste Heat Recovery Of Internal Combustion Engine

Organic Rankine Cycle?ORC?system has been considered as the most potential method to improve thermal efficiency of engines and a key way to reduce CO₂ emissions.It is the main problem to design a compact ORC system with high efficiency and make it match the variable working conditions of vehicle engines.The system compactness and off-design performance of each component cannot be taken into consideration by the traditional analysis method,so the traditional method should be substituted by a through-flow analysis method which can consider the influence of component geometric parameters on system performance.This work proposed a through-flow analysis method of ORC system,which can consider the impact of component main geometric parameters on system performance.A confluent cascade expansion ORC?CCE-ORC?system was designed in this work,and the performance of this system was analyzed under engine full operating conditions.The impact of engine coolant temperature and heat dissipation of exhaust gases were analyzed.This work includes the following aspects.The ORC system through-flow analysis method was established,and the sub mathematic model of plate-fin evaporator,the louver-fin-tube condenser and the turbo expander were established and validated.Based on these method,the control variable and geometric parameters can be optimized together.A CCE-ORC system of a diesel engine was designed.The working fluid selection was analyzed,and the influence of main geometric parameters on system performance was analyzed.Compared with traditional method,the cooperation optimization method can improve system performance by 4.9-10.4%in the engine common operating condition region?engine rotating speed:1100-1400 r/min,engine load:50-100%?.System performance under engine full operating conditions was analyzed,and the results showed that the system net power output will increase as the engine rotating speed or engine load increases.Condensation temperature can be influenced by the ambient temperature,and the system net power output will decrease by about 10%when ambient temperature increases by 5?.Comparing with the baseline engine,the ICE-CCE-ORC combined system can improve engine power by 4.3-8.2%in the engine common operating region,the fuel consumption can be reduced by 4.1-7.5%,and the thermal efficiency of the combined system in that region can be 45.6-48.3%.The impact of engine coolant temperature and heat dissipation of exhaust gases on ORC system performance were analyzed.The results showed that engine coolant temperature rise and heat isolation in exhaust pipes can improve the net power output of ORC system.When the engine coolant temperature is 30?and the thermal insulation effectiveness is 75%,the ORC system net power output can increase by 41.6-78.7%in engine common operating region.The combined system can improve the power of based engine by 8.0-11.9%in engine common operating region,and it can reduce the fuel consumption by 7.4-10.6%.The thermal efficiency of the combined system can be up to47.4-50.0%in this region.